1. Field of the Invention
The present invention relates to a transflective liquid crystal display device provided with transmission and reflection regions in a pixel, and particularly relates to an arrangement configuration of optical members in the transflective liquid crystal display device.
2. Description of the Prior Art
Utilization is advanced in a wide range of fields, such as OA equipment and a portable device, from the feature of small size, a thin shape, and low power consumption in a liquid crystal display. Unlike a cathode ray tube (CRT) or an electroluminescence (EL) display device, the liquid crystal display device does not have a function which emits light itself. Therefore, a backlight source is used for the transmissive liquid crystal display device. The transmissive liquid crystal display device controls its display by switching the transmission/interception of the backlight by use of a liquid crystal panel. The transmissive liquid crystal display device can obtain a bright screen independently of the surrounding environment due to the backlight. However, the backlight source consumes the power largely. Hence, there is a problem in the transmissive liquid crystal display device that the operating time is short, especially when driving with a battery.
Accordingly, in order to solve the above-mentioned power consumption problem of the backlight source, proposed is a reflective liquid crystal display device which displays by use of a surrounding light. This reflective liquid crystal display device is provided with a reflective plate instead of a backlight source, and controls the display by switching the transmission/interception of the surrounding light by use of the reflective plate in a liquid crystal panel. In the-reflective-liquid-crystal display device, in order to use surrounding light, power consumption can be reduced and a miniaturization and a weight saving can be attained. However, in the-reflective-liquid-crystal display device, when surroundings are dark, there is also a problem to which visibility falls.
Then, in order to prevent the increase in the power consumption by the backlight source, and the fall of the visibility by surrounding environment, a transflective-liquid-crystal display device is proposed. The transflective liquid crystal display device is provided with transmission and reflection regions in each pixel, which leads to functioning as both the transflective and reflective liquid crystal display devices. This transmissive liquid crystal display device is provided with an uneven resin layer in a region to be the reflection region on an active matrix substrate. Subsequently, on the resin layer, a reflective film made of a metal film or the like is provided, thus forming a reflective plate which reflects a surrounding light diffusely.
The transflective liquid crystal display device requires letting light come into a liquid crystal layer through the transmission region in a transmission mode. For this reason, one or a plurality of optical anisotropic elements and polarizing plates are disposed on a surface opposite to a liquid crystal holding surface of the active matrix substrate (on the back light side). However, there arises a problem with the transflective liquid crystal display device that the light leakage occurs, when viewed from a diagonal direction during black display (the display in a dark state) when a polymeric stretched film is used as the optical anisotropic element.
Japanese Patent Application Laid-Open No. 2002-311426 (Hereinafter, referred to as Patent Literature 1) discloses a method of preventing the occurrence of such light leakage in a transflective liquid crystal display device. A homogeneous-oriented liquid crystal layer is interposed between first and second substrates in the transflective liquid crystal display device disclosed in Patent Literature 1. Furthermore, a first optical element and a first polarizing plate are disposed on a surface opposite to the liquid crystal layer of the first substrate, and a second optical element and a second polarizing plate are disposed on a surface opposite to the liquid crystal layer of the second substrate. Transmission and reflection regions are formed in the second substrate. A backlight is disposed outside a second polarizing plate. The second optical element includes at least one liquid crystal film. The liquid crystal film has a structure of fixing a nematic hybrid orientation formed in a liquid crystal state of a polymeric liquid crystal substance which shows a positive uniaxiality. Note that the term “nematic hybrid orientation” refers to an orientation pattern in which liquid crystal molecules are nematic oriented and, at this point, the angles formed by the directors of liquid crystal molecules and a film plane are different between the upper and lower surfaces of the film. Incidentally, as shown in FIG. 13, a tilt angle is defined as an angle formed by the liquid crystal molecules, which consist of the liquid crystal layer and the liquid crystal film, and the substrate or a film plane direction, and a tilt direction is defined as a direction which makes the formed angle acute.
In the above-mentioned Patent Literature 1, it is possible to compensate for the anisotropy of a phase contrast caused by pretilt in the liquid crystal layer, by using the liquid crystal film for the second optical anisotropic element. As a result, it is possible to reduce the amount of the light leakage in the diagonal direction upon black display.
In the above-mentioned Patent Literature 1, as shown in FIG. 1, the absorption axis of a first polarizing plate 102 is set to be +105°. The lag axes of a first phase contrast plate 103 and a second phase contrast plate 104, both plates being made of two polycarbonate films which are the first optical anisotropic element, are set to be +30° and +90°, respectively. Then, the Patent Literature 1 discloses the configuration in a manner of setting the tilt direction of a liquid crystal film 108 of the second optical anisotropic element to −90°; the lag axis of a polycarbonate film (a third phase contrast plate 109) of the second optical anisotropic element to +150°, and the absorption axis of a second polarizing plate 110 to +165°. Note that a reference symbol 106 in FIG. 1 denotes the liquid crystal layer.
In Patent Literature 1, as shown in FIG. 2B, it is possible to enlarge a region with high contrast ratio (CR) by specifying the optical axis of each optical member as described above compared with a case of using only a polymeric stretched film (a polycarbonate film) as the second optical anisotropic element (FIG. 2A). However, in the configuration of the optical members shown in FIG. 1 of Patent Literature 1, the optical axis of the liquid crystal film 108 is disposed to be parallel to that of the polycarbonate film (the second phase contrast plate 104) of the first optical anisotropic element. Hence, it is not possible to control the coloring which causes a red tinge upon white display when a viewer changes the viewing angle from the front to the left or right.